Abstract
Flow of glacial ice in the West Antarctic Ice Sheet localizes in narrow bands of fast-flowing ice streams bordered by ridges of nearly stagnant ice, but our understanding of the physical processes that generate this morphology is incomplete. Here we study the thermal and mechanical properties of ice-stream margins, where flow transitions from rapid to stagnant over a few kilometers. Our goal is to explore under which conditions the intense shear deformation in the margin may lead to deformation-induced melting. We propose a 2-D model that represents a cross section through the ice stream margin perpendicular to the downstream flow direction. We limit temperature to the melting point to estimate melt rates based on latent heat. Using rheology parameters as constrained by laboratory data and observations, we conclude that a zone of temperate ice is likely to form in active shear margins.
Highlights
The West-Antarctic Ice Sheet is thought to lose over 80% of its mass [Bamber et al, 2000] through outlet glaciers and arterial drainage routes called ice streams, which are typically about a kilometer thick, tens of kilometers wide and hundreds of kilometers long
The goal of this study is to investigate the possibility of deformation-induced melting in active shear margins
We find that the two data sets provide somewhat conflicting constraints on the size of a potential temperate zone: While the agreement with surface velocities improves for a large temperate zone, the agreement with temperature measurements improves for a small temperate zone
Summary
The West-Antarctic Ice Sheet is thought to lose over 80% of its mass [Bamber et al, 2000] through outlet glaciers and arterial drainage routes called ice streams, which are typically about a kilometer thick, tens of kilometers wide and hundreds of kilometers long. Further evidence that ice-stream width is not controlled by topography alone comes from evidence that some margins have shifted in the past [Jacobel et al, 1996; Clarke et al, 2000; Fahnestock et al, 2000; Jacobel et al, 2000] or are migrating currently [Bindschadler and Vornberger , 1998; Harrison et al, 1998; Echelmeyer and Harrison, 1999] These observations suggest that a physical mechanism must exist that selects the location of the margin and the flow speed of the stream self-consistently. Measurements of shear stresses in the margins of the Ross Ice Streams [Joughin et al, 2002] and a laboratory study of ice cores retrieved from depth [Jackson and Kamb, 1997] confirmed that a significant portion of the driving stress is balanced by stresses on an approximately vertical interface parallel to the edge of the ice stream. We refer to these lateral boundaries of ice streams, where the surface velocity drops by two to three orders of magnitude over as little as a few kilometers, as the shear margins
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